Stabilized light-sensitive silver halide emulsions



3,161,5i Patented Dec. 15, 1964 3,161,515 STABILHZED LiGli-iT-SENfilTiVE SILVER HAHDE EMULSEQNfi John A. Welsh, Binghainpton, NEL, assignor to Generai Aniline & Film Corporation, New York, N.Y., a corporation of Deiaware No Drawing. Filed Dec. 18, 1962, Ser. No. $55,376 5 (Ilairns. {8. 96-66} The present invention relates, in general, to photography and, in particular, to stabilized photographic emulsions.

It is Well known that light-sensitive emulsions, such as gelatin silver halide emulsions, have a'decided tendency to fog. The fog may be of two types, namely, yellow fog and chemical (gray) fog. The yellow fog, sometimes referred to as color fog or dichroic fog, is essentially a colloidal deposit of silver, the color intensity and general appearance of which are determined by the minute particle size and degree of subdivision. The fog is chiefly yellow in color and is most apparent in the light portions of a negative. The color may vary, however, and the colloidal silver particles may, for example, appear green by reflected light, and yellow or red by transmitted light. The so-called chemical fog, or gray fog, on the other hand, is the more common and is formed in a number of ways. It may be caused by premature exposure, by excessive ripening of the emulsions, or by storage of the film at high temperatures or for unusually long periods of time.

Accordingly, it is an object of this invention to provide a stabilizer for silver halide emulsions.

Another object of this invention is to provide a stabilizer or fog inhibiting agent as an ingredient in silver halide emulsions to prevent'the formation of fog in lightsensitive silver halide emulsions.

Still other objects and advantages of the invention will become further apparent from the following detailed de-';

scription of the invention.

The above and other objects of the invention are accomplished' in accordance with the present invention by incorporating into a layer of a photographic element a 4,6-dihydroxypyraz0le(3,4d)pyrimidine or 4-hydroxy-6- mercapto-4-hydroxypyrazole(3,4d)pyrimidine of the structural formula:

LEI: N -i v t I OH The pyrimidine derivatives utilized for the purposes of this invention are prepared from 3-aminopyrazole-4-carboxyamide hemisulfate by heating the same with urea or thiourea at an elevated temperature in accordance with the procedure set forth and described in 1 our. Am. Chem.

'Soc., vol. 78, p. 788.

The stabilizers are also useful when added to photographic silver halide developer solutions used in the development of imagewise exposed silver halide emulsions.

In addition to being useful in orthochromatic and panchromatic emulsions, the stabilizers can also be used in non-sensitized emulsions, X-ray emulsions, paper emulsions, color emulsions and the like. If used with sensitizing dyes, they can be added to the emulsion before or after the dyes are added.

The stabilizers may also be employed in conjunction with known antifoggants and stabilizers, reduction sensitizers, metal and noble metal sensitizers, or in combination with other additive agents and the like.

The stabilizers may also be employed in gelatin or other colloid, such as polyamides or a mixture of gelatin with a polyamide as described in United States Patent 2,289,- 775; polyvinyl alcohol and jelling compound as described in United States Patent 2,249,537; polyvinyl acetaldehyde acetal resins and partially hydrolyzed acetate resins described in United States Patents 1,939,422 and 2,036,- 092; cellulose derivatives, e.g., cellulose nitrate, cellulose acetate, and the lower fatty acid esters of cellulose includ ing simple and mixed esters and ethers of cellulose, and the like, as an under or overcoat for the emulsion, or as a backing layer for the support.

In the preparation of an emulsion containing the stabilizers in accordance with the invention, a solution of the stabilizer in a suitable solvent, such as water, alcohol, di methyl formamide, or alcohol-Water mixture, adjusted to a neutral or slightly alkaline pH, i.e., about 7.5 to 10, is made up and the solution mixed with the emulsion at any point during its preparation, but preferably during ripening or just prior to coating in concentrations varying from 5 to 500 milligrams (preferably from 20 to 200 milligrams) per liter of emulsion depending on the type of emulsion employed. Expressed in terms of silver halide present in the emulsions, the above amounts correspond essentially to 0.6 mol of silver halide.

The method of testing the stabilizers in the following examples consists of coating several film supports, such The following examples will serve to illustrate the practice of the invention.

PREPARATION I 4,6-Dihydr0xypyrazole(3,4d)Pyrimidine uerrA os Five grams of 3-aminopyrazole-4-carboxamide hemisulfate was mixed with 10 grams of urea of formamide and heated in a metal bath at C. for 30 minutes until the clear melt became mushy. The heat was then increased to 190-195 C. for 20 minutes when the melt became solid. After cooling, the solid was dissolved in 50 cubic centimeters of 1 N sodium hydroxide, boiled for minutes, and filtered. The filtered product was reheated to boiling and acidified with glacial acetic acid at a pH of 5.0. The precipitated solid provided 2.6 grams of 4,6-dihydroxypyrazole(3,4d)pyrimidine as a White product.

PREPARATION H 4-H ydroxy-o-M ercaptopyrazole (3,4d pyrimidine Five grams of 3-aminopyrazole-4-carboxamide hemisulfate was mixed with grams of thiourea in a round bottom flask and heated in a metal bath at 165 C. until the clear melt became mushy. The heat was then increased to 190-200 C. Heating was continued until the contents of the flask became quite solid. The solid product was cooled and dissolved in 50 cubic centimeters of 2 N sodium hydroxide, charcoal was added, and the solution boiled for 5 minutes. The solution was filtered, reheated to boiling and acidified to a pH of 5.0 with glacial acetic acid. A yellowish-white product in a yield of 2.5 grams was obtained.

EXAMPLE I The stabilizer of Preparation I was incorporated into a boil type high-speed silver bromoiodide emulsion in a concentration of 50 cubic centimeters of a 1% by weight solution to 10 kilograms of emulsion along with saponin as a wetting agent. A control consisting of an unstabilized emulsion and one containing a conventional commercially used stabilizer in a concentration of 100 cubic centimeters of a 2% by weight solution per 10 kilograms of emulsion. Three photographic films coated with three abovedescribed emulsions and stored in an incubator for 6 days at 50 C. at 80% relative humidity, imagewise exposed, were developed in an Ansco A-47 developer, fixed and washed under the same conditions. The fog density produced in the unexposed areas of the three emulsions was measured and the following results were found:

The Ansco A-47 developer had the following compo- Water to make 1 liter.

EXAMPLE II Example I was repeated with the exception that the 4,6- dihydroxypyraz0le(3,4d) pyrimidine was replaced by an equal quantity of 4-hydroxy-6-mercaptopyrazole(3,4d)pyrimidine. The results obtained were essentially identical with those of Example I.

EXAMPLE III Example I was again repeated with the exception that the stabilizer 4,6-dihydroxypyrazole(3,4d)pyrimidine was incorporated into an ammonia type X-ray emulsion at a concentration of cubic centimeters of the 1% by Weight solution per 10 kilograms of emulsion with similar results. Development was carried out in an Ansco A-30 developer having the following composition:

Grams p-Methylaminophenol sulfate 3.5 Sodium sulfite (anhydrous) 60 Hydroquinone 9 Sodium carbonate (monohydrated) 40 Potassium bromide 2 Water to make 1 liter.

EXAMPLE IV Example I was again repeated with the exception that the stabilizer 4-hydroxy-6-mercaptopyrazole(3,4d)pyrimidine was incorporated into a high contrast graphic art emulsion at a concentration of 100 cubic centimeters of the 1% by weight solution per 10 kilograms of emulsion with similar results. Development was carried out in a graphic arts developer identified as Ansco A-79 and having the following composition:

Grams Sodium sulfite (anhydrous) 3O Paraformaldehyde 7.5 Potassium metabisulfite 2.5 Boric acid crystals 7.5

Hydroquinone 22.5 Potassium bromide 1.5 Water to make 1 liter.

The film strip containing the antifoggant of this invention did not lose speed and contrast and showed considerably less fog than the two comparison samples.

Various modifications of the invention will occur to persons skilled in the art. Thus, it is evident that in lieu of using the compound of the specific examples, any of the compounds mentioned in the specification can be readily employed with similar results. Therefore, it is not intended that the invention be limited in the patent granted except as necessitated by the appended claims.

What is claimed is:

l. A light-sensitive silver halide emulsion containing in a stabilizing and antifogging amount, a compound of the following formula:

wherein Y is a member of the group consisting of oxygen and sulfur.

2. A light-sensitive silver halide emulsion as recited in claim 1, wherein the concentration of the stabilizer varies from 5 to 500 milligrams per liter of emulsion.

3. A light-sensitive photographic material comprising a base and a light-sensitive silver halide emulsion, said light-sensitive material containing a stabilizer therefor, 4,6-di-hydroxypyrazole(3,4d)pyrimidine in an antifogging amount.

4. A light-sensitive photographic material comprising a base and a light-sensitive silver halide emulsion, said light-sensitive material containing 6-rnercapto-4-hydroxypyrazole(3,4d) pyrimidine in a stabilizing and antifogging amount.

5. A process of preventing the formation of fog in a silver halide emulsion which includes carrying out the development of the imagewise-exposed silver halide emulwherein Y is a member of the group consisting of oxygen sion in the presence of a compound of the following and sulfur.

structural formula:

. References Cited in the file of this patent H N 5 5 UNITED STATES PATENTS Y 2,173,628 Kendall Sept. 19, 1939 H H 2,403,927 Kendall et a1 July 16, 1946 3,040,047 Sirakawa June 19, 1962 

1. A LIGHT-SENSITIVE SILVER HALIDE EMULSION CONTAINING IN A STABILIZING AND ANTIFOGGING AMOUNT, A COMPOUND OF THE FOLLOWING FORMULA: 